As the Oakland Athletics played last summer between June 30 and July 8, fans in Oakland's McAfee Stadium knew they were watching their team struggle through a rough patch that would see their beloved A's drop seven out of 10 games. What they didn't know was that they—as well as all of the players and ballpark workers—were also participating in an elaborate homeland-security experiment.

Throughout that entire home stand, researchers from nearby Sandia National Laboratories in Livermore, Calif., were scattered around the stadium, fiddling with strange gadgets the size of large tool chests. Their mission: to sniff and profile the rich ballpark air for signs of hazardous materials or substances that could confuse a chemical sensor into sounding a false alarm. "This was the opportunity for us to look at common benign chemicals and confirm that our system would not confuse them with toxic chemicals," says Ben Wu, a chemical engineer at Sandia, and the project's lead researcher. "Those tests cannot be duplicated in the laboratory."

With the war on terrorism now in its sixth year, public places such as sports stadiums, parks and shopping malls remain highly vulnerable to swift and potentially lethal chemical attacks. That's largely because accurate and reliable broad-spectrum detection systems are still a rarity. "Environmental chemical detection is an area that greatly concerns the government, businesses and the public, yet few deployable systems are available," says Greg Allmendinger, president of Harbor Research, a consulting and research company that covers security issues. "Everybody's still in the lab; there's not very much deployed."

But that may change soon. Researchers are working hard to reduce the size and cost of sensors, so they can be combined with RFID devices that can be linked in an ad hoc network. Because the sensors will be inexpensive and linked wirelessly, they'll be able to cover a broad area. At Sandia, researchers are putting the final touches on the Rapidly Deployable Chemical Detection System (RDCDS), the U.S. government's planned key tool for sensing the presence of hazardous substances in public places. The system, which is funded by the U.S. Department of Homeland Security, is designed to provide rapid and effective protection at venues that attract large numbers of people. It uses wireless-network technology and can be deployed with as little as 24 hours' notice.

As a "detect-to-warn" technology, RDCDS aims to quickly alert emergency responders to a chemical release, reducing response times and thereby minimizing casualties. "Typically, with the chemicals we're concerned about, the health effects are very rapid," says Bill Replogle, manager of advanced-systems deployment at Sandia. "You would see people in distress as soon as they started to breathe it, so you want to detect it as soon as possible."